Blood fractionation is important in clinical chemistry. Chromogenic analysis is used to determine the concentration of particular components dissolved in the blood. The presence of a particular component is signaled by color production or color change. The presence of erythrocytes (RBC's) in the whole blood disturbs the reading of the chromogenic analysis due to the turbidity and color of the whole blood. It is therefore an object of the present invention to develop a simple and cost effective method for removal of the RBC's in the whole blood prior to the use of the remaining serum or plasma in the analysis of dissolved blood components.
Previous investigators have described methods for separating plasma or serum from whole blood. EPO Publication No. 325413 to Jeong et al. describes a method and device for separating plasma from RBC's which involves contacting a polycationic surface with whole blood and having the RBC's bind to the surface leaving the plasma free of RBC's. Steric chromatography is used to separate plasma or serum components from whole blood in U.S. Pat. No. 3,657,116 to Haller. The plasma or serum is prefractionated using a precipitant. The precipitant-containing plasma or serum fraction is introduced into a porous-glass filled chromatographic column and the plasma or serum is thereby separated from the precipitant. U.S. Pat. No. 4,786,603 to Weilinger et al. describes coagulation-neutral hydrophilic glass fibers which can be used for the separation of plasma from whole blood. Additionally, U.S. Pat. No. 4,477,575 to Vogel et al. describes a composition and process for separating plasma or serum from whole blood wherein the whole blood is passed through a layer of glass fibers and the plasma or serum that is separated from the whole blood becomes available at the other side of the layer.
Other workers have described devices which both separate out the RBC'S from a whole blood sample and analyze the resultant plasma or serum for a particular dissolved component. EPO Publication No. 287731 to Maddox describes a dry test device comprising an absorbent reagent zone containing a chemical assay or immunoassay and an analyte target having a polysaccharide material that can limit the passage of RBC's or hold the RBC's on or near the surface of the absorbent reagent zone. A one-step procedure, employing simultaneous separation of fluid from whole blood with testing for a desired component is described in U.S. Pat. No. 4,678,757 to Rapkin et al. Blood is applied to the surface of a carbohydrate-treated carrier. The fluid portion migrates away from the point of contact and the cellular components remain in close proximity to the point of contact. If the carrier is further treated with a reagent employed to detect a component, a color will appear in the fluid. U.S. Pat. No. 3,552,928 to Fetter describes a means for separation of whole blood into a colorless fluid and a red cell or residue component. The whole blood is contacted with a separative reagent (a water-soluble, non-volatile amino acid), the residue is removed and the remaining fluid can be contacted with a test reagent. Both reagents may be contained on a single matrix (i.e. bibulous filter paper), however, the matrix must allow the colorless fluid to flow from the separating reagent to the test reagent.